1) Field of the Invention
This invention relates to an overhead work suspension conveyor for carrying a piece of work such as a tailgate to a main body in a vehicle body assembly line or the like.
2) Description of the Related Art
When tailgates are carried to and assembled on main bodies in a vehicle body assembly line, it has been the conventional practice to carry the tailgates in a predetermined spatial orientation from a tailgate storage to the assembly line.
Tailgates and trunk lids are large components, vary in configuration and size from one car type to another, and cannot be stably stacked one over another. Moreover, a work conveyor of a vehicle body assembly line is generally arranged at a high altitude, for example, on a ceiling to effectively use the space of a plant.
To carry pieces of work from a work storage, which is arranged at a low altitude, for example, on the floor of the plant, to such a work conveyor provided at a high altitude, a drop lifter is generally used. As an alternative, such work pieces are carried by plural workers.
As described above, tailgates and trunk lids are however large components, vary in configuration and size from one car type to another, and cannot be stably stacked one over another. It is therefore impossible to automatically carry them by a drop lifter. Their transportation by workers requires substantial labor.
In the meantime, a suspension conveyor has been proposed in Japanese Patent Application Laid-Open No. SHO 61-178308. The conveyor comprises a movable member guided along a horizontal rail and a plurality of hanger frames secured on the movable member. Each of the hanger frames is adapted to convey a piece of work in a suspended position. Each hanger frame is provided with receivers each of which can be selectively moved between a work suspending position and a work nonsuspending position depending on the car type of work piece, whereby the suspension conveyor has made it possible to convey work pieces of different car families.
The above suspension conveyor, however, is not designed to convey pieces of work up and down. More-over, the change-over of the plural receivers between their work suspending positions and their work nonsuspending positions must be manually conducted by workers. When pieces of work to be conveyed are frequently changed from one car type to another, the suspension conveyor develops the problem that the work efficiency is very impaired.